The present invention relates to portable audio devices, and more particularly, relates to portable audio devices capable of communicating with external audio systems to provide enhanced audio playback.
Advances in digital electronic technology have led to a rapid growth in portable audio devices. In particular, portable audio devices such as audio CD players, digital audio players, FM/AM radio receivers, televisions, and DVD players have become increasingly popular among consumers as they have become small, lightweight, and easy for an individual to carry. Most such devices include small, built-in speakers or provide attached headphones that, in some instances, offer relatively good audio quality.
However, the size limitations of speakers for such devices significantly limit their ability to generate significant sound pressure levels across the full audio range. More particularly, small speakers commonly used in portable audio devices, or in audio headphones intended for attachment to such devices, simply cannot generate significant bass output. As a result, audio playback often lacks the full range sound available from audio systems employing full-size speakers. Such full-size speakers use one or more relatively large audio drivers, commonly referred to as “woofers” or “sub-woofers,” to generate the lower frequency components of an audio signal. While no specific frequency cutoffs exist, frequency components below 100 Hz and extending down to 20 Hz or lower are commonly regarded as the bass components of an audio signal. At these frequency ranges, there is simply no substitute for physically large, high-powered audio drivers, which practically cannot be included in a portable audio device.